1. Field of the Invention
The present invention relates to a projection display device such as a projector etc., and more specifically to a projection display device for displaying an image by projecting the image on the screen etc. using a display device.
2. Description of the Related Art
Conventionally, a lamp light source such as an extra high pressure mercury lamp etc. has been used as a light source of a projection display device using a display device. Since such a lamplight source is short-life, a maintenance operation such as exchanging a lamp is frequently performed. In addition, when color images are displayed, it is necessary to provide, for example, an optical system for taking out red light, green light, and blue light from white light emitted from a lamp light source. Therefore, the device configuration is complicated and the light use efficiency is reduced.
On the other hand, although a projection display device using an LED light source has been proposed as a light source, it is low in the light use efficiency of the LED, thereby failing in attaining sufficient luminance on the displayed image.
Therefore, there has been an attempt to use a laser light source such as a semiconductor laser etc. as a light source of a projection display device. Since the laser light source is longer-life than the lamp light source, maintaining operations are not required substantially. In addition, since laser light can be directly modulated depending on a displayed image when the laser light source is used, the device configuration is simple and the light use efficiency can be improved. Furthermore, using a laser light source, a larger color reproduction area can be obtained.
However, a laser light source has high coherence. Therefore, when a laser light source is used as a light source of a projection display device, a pattern of high-contrast spots such as a speckle, speckle noise, speckle patterns, etc. (hereinafter referred to simply as “speckle”) is formed on the screen, thereby degrading the quality of displayed images. Therefore, when a laser light source is used as a light source, it is important to reduce the speckle. Accordingly, the technology of reducing the speckle has been proposed in the following variations.
FIG. 1 is a schematic diagram of an operating illumination device disclosed by the patent document 1 (Japanese Laid-open Patent Publication No. 2005-301164). An illumination device 101 illustrated in FIG. 1 includes a laser light source 102, an electromagnet 103, an oscillation plate 104 and a diffusion plate 105. The oscillation plate 104 is arranged opposite the electromagnet 103, and made by a magnetic material. The diffusion plate 105 is arranged at one end of the oscillation plate 104, and the laser light emitted from the laser light source 102 enters the diffusion plate 105. Then, the diffusion plate 105 vibrates substantially perpendicularly to the laser light emission direction from laser light source 102 based on the operation of the electromagnet 103, thereby reducing the speckle.
FIG. 2 is an explanatory view of the rough configuration of the projector disclosed by the patent document 2 (Japanese Laid-open Patent Publication No. 2008-191279). A projector 111 illustrated in FIG. 2 includes a light source (laser light source devices 112R, 112G, and 112B), an intermediate image forming unit (first projection optical system 113), an optical system for forming images (second projection optical system 114), and a diffusibility change unit (second diffusion element 115, rotation drive unit 116). The light source emits a coherent light. The intermediate image forming unit forms an intermediate image using the light from the light source. The optical system for forming images forms an image on the display surface with the light from the intermediate image. The diffusibility change unit has a diffusing surface in the position shifted from the intermediate image forming surface on which an intermediate image is formed, and in the position of the optical path from the intermediate image forming unit to the optical system for forming images including the intermediate image forming unit, and changes with time the diffusibility on the surface along the diffusing surface. Then, by the operation of the diffusibility change unit, the speckle is to be reduced.
FIG. 3 is an explanatory view of the behavior etc. of the light in the optical system of the projector disclosed by the patent document 3 (Japanese Laid-open Patent Publication No. 2008-122823). The optical system illustrated in FIG. 3 includes a light source unit 121 for providing coherent light, a spatial light modulation device 123 for modulating the coherent light from the light source unit 121 depending on the image signal and emitting the light from an emission unit 122, and a diffusion unit 124 for diffusing the light from the emission unit 122 by a transmission. The diffusion unit 124 is provided and operated in a position close to the emission unit 122 so that the speckle can be reduced.
FIG. 4 illustrates a coherent light display device having a diffusion element as disclosed by the patent document 4 (Japanese Laid-open Patent Publication No. 06-208089). In the device illustrated in FIG. 4, the coherent light is transmitted through a rotary diffusion element 132 to illuminating the spatial light modulator 131. The rotary diffusion element 132 moves on a screen 133 at a speed at which an interference pattern cannot be detected by human eyes, thereby reducing the speckle.